Add custom support structures tweak

[JoshuaYates]

Hello,

It's not so much a feature needed but more of one which just needs looking at.

When adding support material using the Add new support structures tool, when I click and hold the left mouse button to rotate the part, it adds the support material and rotates the part which makes this feel more like a bug then something which should be in the software and was wondering if this is something which can be removed so it doesn't add the support material when I click and hold the mouse button. This is annoying as I tend to forget to move my mouse away from my model to rotate and end up with random support materials all over the place.